sigprocmask(2)

NAME

sigprocmask — examine and change blocked signals

SYNOPSIS

#include <signal.h> 

int sigprocmask( 
     int how, 
     const sigset_t *set, 
     sigset_t *oset 
); 

DESCRIPTION

The sigprocmask() function allows the calling thread to examine and/or change its signal mask.

If the argument set is not a null pointer, it points to a set of signals to be used to change the currently blocked set.

The argument how indicates the way in which the set is changed and consists of one of the following values:

SIG_BLOCK: The resulting set will be the union of the current set and the signal set pointed to by set.
SIG_SETMASK: The resulting set will be the signal set pointed to by set.
SIG_UNBLOCK: The resulting set will be the intersection of the current set and the complement of the signal set pointed to by set.

If the argument oset is not a null pointer, the previous mask is stored in the location pointed to by oset. If set is a null pointer, the value of the argument how is not significant and the thread's signal mask is unchanged; thus the call can be used to inquire about currently blocked signals.

If there are any pending unblocked signals after the call to sigprocmask(), at least one of those signals will be delivered before the call to sigprocmask() returns.

It is not possible to block those signals which cannot be ignored. This is enforced by the system without causing an error to be indicated.

If any of the SIGFPE, SIGILL, or SIGSEGV signals are generated while they are blocked, the result is undefined, unless the signal was generated by a call to kill() or raise().

If sigprocmask() fails, the thread's signal mask is not changed.

RETURN VALUE

Upon successful completion, sigprocmask() returns 0. Otherwise -1 is returned, errno is set to indicate the error, and the thread's signal mask will be unchanged.

ERRORS

The sigprocmask() function will fail if:

EINVAL: The value of the how argument is not equal to one of the defined values.
EFAULT: set or oset points to an invalid address. The reliable detection of this error is implementation dependent.

APPLICATION USAGE

Threads Considerations

Since each thread maintains its own blocked signal mask, sigprocmask() modifies only the calling thread's blocked signal mask.

For more information regarding signals and threads, refer to signal(5).

LWP (Lightweight Processes) Considerations

sigprocmask() modifies only the calling LWP's blocked signal mask.

AUTHOR

sigprocmask() was derived from the IEEE POSIX 1003.1-1988 Standard.

CHANGE HISTORY

First released in Issue 3.

Entry included for alignment with the POSIX.1-1988 standard.

STANDARDS CONFORMANCE

sigprocmask(): AES, SVID3, XPG3, XPG4, FIPS 151-2, POSIX.1